In order to ascertain an appropriate design an accurate manufacturing process is of particular significance for ophthalmic lenses for vision correction, such as, e.g. contact lenses, intra-ocular lenses, corneal onlay lenses and corneal inlay lenses. In order to inspect physical properties of ophthalmic lenses, such as, e.g. a thickness profile, in the past it was necessary to physically cut up the ophthalmic lens along one or more meridians and then obtain an image of the cross-sections of the ophthalmic lens. More recently, a non-destructive testing method has been suggested, namely the application of Optical Coherence Tomography (OCT) for determining physical properties of ophthalmic lenses.
Optical Coherence Tomography (OCT) is an established medical imaging method, in which light of relatively short coherence length is applied to a scattering sample, and with the aid of an interferometer the distances to scattering points of the sample are inspected. The sample is scanned point by point and from the resulting interference patterns a high resolution image of the scanned sample may be deduced. Optical Coherence Tomography is a fast growing imaging technique that has found wide application especially in the biomedical field.
For the inspecting of their physical properties ophthalmic lenses may be scanned using Optical Coherence Tomography such as, e.g. Frequency Domain OCT, Fourier-Domain OCT, complex Fourier OCT, Optical Frequency-domain imaging or swept-source OCT. In the prior art a method for the inspection of ophthalmic lenses using Optical Coherence Tomography has been suggested, which involves adding a scattering agent to the manufactured ophthalmic lens, e.g. by submerging the manufactured ophthalmic lens in a solution including the scattering agent, and then scanning the ophthalmic lens using Optical Coherence Tomography. By submerging the ophthalmic lens in a solution including the scattering agent, usually a pigment, the anterior surface and the posterior surface of the ophthalmic lens, respectively, are altered by the pigments which adhere to or are embedded within the surfaces. As such, these known methods of inspecting ophthalmic lenses using Optical Coherence Tomography are not really non-destructive methods, because the tested sample ophthalmic lens usually must be discarded. Besides being not really non-destructive the known prior art inspection methods of ophthalmic lenses usually suffer the disadvantage of a rather low signal-to-noise ratio, which hinders an easy inspection of physical properties of the ophthalmic lens.
It is therefore an object of the present invention to provide a factual non-destructive method for inspecting an ophthalmic lens using Optical Coherence Tomography (OCT). It is a further object of the invention to improve the signal-to-noise ratio of the OCT image to enable accurate inspection of the physical properties of interest of the ophthalmic lens.